Re: [PATCH 2/3] kvm hypervisor : Add hypercalls to support pv-ticketlock

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



On Wed, Jan 19, 2011 at 10:53:52AM -0800, Jeremy Fitzhardinge wrote:
> > I didn't really read the patch, and I totally forgot everything from
> > when I looked at the Xen series, but does the Xen/KVM hypercall
> > interface for this include the vcpu to await the kick from?
> >
> > My guess is not, since the ticket locks used don't know who the owner
> > is, which is of course, sad. There are FIFO spinlock implementations
> > that can do this though.. although I think they all have a bigger memory
> > footprint.
> 
> At least in the Xen code, a current owner isn't very useful, because we
> need the current owner to kick the *next* owner to life at release time,
> which we can't do without some structure recording which ticket belongs
> to which cpu.

If we had a yield-to [1] sort of interface _and_ information on which vcpu
owns a lock, then lock-spinners can yield-to the owning vcpu, while the
unlocking vcpu can yield-to the next-vcpu-in-waiting. The key here is not to
sleep when waiting for locks (as implemented by current patch-series, which can 
put other VMs at an advantage by giving them more time than they are entitled 
to) and also to ensure that lock-owner as well as the next-in-line lock-owner 
are not unduly made to wait for cpu. 

Is there a way we can dynamically expand the size of lock only upon contention
to include additional information like owning vcpu? Have the lock point to a
per-cpu area upon contention where additional details can be stored perhaps?

1. https://lkml.org/lkml/2011/1/14/44

- vatsa
--
To unsubscribe from this list: send the line "unsubscribe kvm" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html


[Index of Archives]     [KVM ARM]     [KVM ia64]     [KVM ppc]     [Virtualization Tools]     [Spice Development]     [Libvirt]     [Libvirt Users]     [Linux USB Devel]     [Linux Audio Users]     [Yosemite Questions]     [Linux Kernel]     [Linux SCSI]     [XFree86]
  Powered by Linux